1. Technical Field
The present invention relates, in general, to inspection processes and, more particularly, to mask defect inspection processes.
2. Background Art
Semiconductor devices and integrated circuits are fabricated on semiconductor chips. A fabricated semiconductor chip has both active and inactive areas. The active areas are the areas in which actual semiconductor device or circuit features are formed, whereas the inactive areas do not have an actual device or circuit formed thereon. An inactive area can be located between adjacent active areas and/or on the periphery of the chip.
Photolithography is widely used in semiconductor device fabrication. In a photolithography process, a pattern is formed on a photoresist layer over a semiconductor chip using a mask. Through the pattern in the photoresist layer, an etching process forms structures, e.g., openings in dielectric layers, trenches in the semiconductor substrate, etc., on the chip. The etching process is often followed by other fabrication steps such as, for example, dopant implantation, oxide growth, chemical vapor deposition, metal deposition, polishing, and the likes. The quality of the mask can have significant effects on the reliability, performance, and yield of the semiconductor devices and/or circuits fabricated on the chip. Therefore, the mask is routinely inspected for defects. A defective mask is either repaired to restore its quality or scrapped and replaced.
During a mask inspection process, the mask is compared with a design layout that generated the mask. If a mismatch between a pattern on the mask and the design layout data exceeds a predetermined criterion, the mask is considered defective. The inspection process does not distinguish between patterns in active areas and patterns in inactive areas. However, the semiconductor device fabrication process is significantly more sensitive or intolerable to mismatches in the active areas than to mismatches in the inactive areas. In addition, the fabrication process can have different sensitivities to mismatches in different portions of the active areas. In order to ensure high quality, performance, reliability, and yield, the mismatch criterion is conventionally established according to the most sensitive or least tolerable pattern features in the active areas. Consequently, a mismatch in the inactive areas that has insignificant effect on the device performance can render the mask defective. This will result in unnecessary scraps and/or repairs of the mask, thereby increasing the cost and cycle time of the semiconductor device fabrication process.
Accordingly, it would be advantageous to have a mask inspection process that improves the time efficiency and cost efficiency of semiconductor device fabrication processes. It is desirable for the process to be simple and easy to implement. It would of further advantage for the process to be compatible with existing mask inspection apparatuses.
Generally, the present invention provides a process for inspecting an object. By way of example, the object is a mask or a reticle used in a photolithography process, and the process inspects the mask to detect defects in the patterns on the mask. In accordance with the present invention, the inspection process establishes at least two defect criteria or margins. A first criterion or margin is associated with patterns in a more sensitive or critical area on the mask, and a second criterion or margin is associated with patterns in a less sensitive or critical area on the mask. The first criterion is stricter than the second criterion. In other words, the first margin is smaller than the second margin. The inspection process rejects the mask as defective if a mismatch between a pattern in the more critical area and the predetermined design data exceeds the strict first criterion. The inspection process also rejects the mask as defective only if a mismatch between a pattern in the less critical area and the predetermined design data exceeds the relaxed second criterion. Therefore, the inspection process is able to maintain a high standard on the mask in the more critical areas and relax the standard in the less critical areas. Consequently, the quality of the mask is ensured without incurring unnecessary repair and scrap costs of the mask and the photolithography process.